Method for production of porous cross-linked polymer material

ABSTRACT

In producing a porous cross-linked polymer by forming a water-in-oil type high internal phase emulsion and subsequently polymerizing the emulsion, a method for the production of a porous cross-linked polymer material which comprises a step of polymerizing a water-in-oil type high internal phase emulsion obtained in the presence of a polyglycerine fatty acid ester. This invention permits an HIPE to be polymerized at a high temperature for the purpose of stabilizing the HIPE and consequently warrants quick production of a porous cross-linked polymer material possessed of an excellent water absorbing property.

TECHNICAL FIELD

This invention relates to a method for the production of a porouscross-linked polymer material by the use of a polyglycerine fatty acidester as a surfactant.

BACKGROUND ART

As a technique for obtaining a porous substance formed of uniform opencells of a minute diameter, a method for obtaining the polymer in awater-in-oil type high internal phase emulsion (hereinafter referred tobriefly as “HIPE”) in the presence of a specific surfactant has beenknown. It is generally held that the term “high internal phase emulsion”as used herein means an emulsion in which the ratio of the internalphase to the total volume of the emulsion exceeds 70 vol. % [K. J.Lissant, Journal of Colloid and Interface Science, Vol. 22, 462 (1966)].U.S. Pat. No. 5,334,621, for example, discloses a method for producing aporous material by cross-link polymerizing a polymerizing monomercontained in the HIPE (hereinafter referred to the “HIPE method”).

This HIPE method produces a porous cross-linked polymer by preparing anHIPE containing (i) a polymerizing monomer mixture containing anoil-soluble vinyl monomer and a cross-linking monomer possessed of notless than two functional group in the molecular unit, (ii) a water phaseaccounting for 90 wt. %, preferably 95 wt. %, and particularlypreferably 97 wt. % of the emulsion, (iii) a surfactant active agentsuch as a sorbitan fatty acid ester and a glycerol mono-fatty acidester, and (iv) a polymerization initiator and heating the HIPE till itis polymerized and cross-linked. Generally, the porous cross-linkedpolymer is produced by mixing the oil phase containing at least thecomponents (i) and (iii) mentioned above and the water phase, namely thecomponent (ii), and emulsifying the resultant mixture thereby preparingan HIPE and adding an initiator, namely the component (iv), to the HIPEand, at the same time, heating them together to a temperature mostsuitable for the polymerization of the HIPE and initiating thispolymerization. According to this HIPE method, since a porous materialformed of open cells in a reticular pattern by a reversed-phase emulsionpolymerization, the produced porous material is fated to acquire suchcharacteristic properties as low density, water absorbing property,water retaining property, heat insulating property, and sound insulatingproperty.

As a technique for preparing such an HIPE, the official gazette ofWO97/45456, for example, discloses a method for preparing this HIPE byemulsification using at least one sorbitan fatty acid ester or sugarfatty acid ester with a view to stabilizing the HIPE. Though it has nomention of the temperature for the preparation of the HIPE, it has astatement to the effect that when the HIPE is in a stable range, it canbe cured, namely polymerized, at a temperature in the range of 25-90° C.In fact, when sorbitan monolaurate and ditallow dimethyl ammoniumchloride are used in combination, an HIPE is prepared by using a waterphase at 40° C. and the HIPE is polymerized at 70° C. for 24 hours toproduce a polymer material.

The official gazette of WO97/45479 discloses a method for preparing anHIPE by using an emulsifier system composed of an anionic surfactantpossessed of an oleophilic moiety and an anion group and a quaternarysalt possessed of a hydrocarbon group of not less than eight carbonatoms. Though it has no mention of the temperature for preparing theHIPE, it has a statement to the effect that the HIPE can be cured,namely polymerized, at least at a temperature of not less than 25° C.

The HIPE method, as described above, obtains a porous cross-linkedpolymer by emulsifying an oil phase containing at least one species ofpolymerizing monomer and a water phase by the use of an emulsifier suchas a surfactant and then polymerizing the resultant HIPE by means ofheating. Where this process is performed continuously, it is necessaryfor the purpose of exalting the efficiency of production to shorten thetime for preparing an HIPE and the time for subsequently polymerizingthe HIPE. Generally the HIPE is prepared in an emulsifying device andthen the HIPE is polymerized in a polymerizing device. Where thepolymerization of the HIPE is initiated by adding a polymerizationinitiator to the HIPE and subsequently heating the HIPE containing thepolymerization initiator, therefore, the fact that the temperature ofthe HIPE in the emulsifying device and the polymerization temperature ofthe HIPE in the polymerizing device are approximated closely to eachother is believed to bring the advantage of curtaining the time forinitiating the polymerization of the HIPE.

Since the HIPE generally contains such a large amount of water that thewater content thereof reaches a level in the range of 1,000-25,000 (v/v)%, however, it is extremely deficient in stability and is deprived ofstability even by a slight increase of temperature. Normally, therefore,the practice of preparing an HIPE by emulsifying an oil phase containingin advance therein a polymerization initiator and a water phase at atemperature in the range of 25-40° C. has been in vogue. Such is thetrue state of affairs.

Further, when a porous cross-linked polymer is produced by polymerizingan HIPE, the charged raw materials possibly succumb to degeneration andconsequently emit offensive odor. Since the degeneration of this sortdepends particularly on temperature, it is naturally preferable toprepare the HIPE at a low temperature for the purpose of preventing thecomponents used in the HIPE from generating to such degeneration. Inconsideration of the instability of the HIPE due to elevation oftemperature as a contributory factor, the preparation of the HIPEinclusive of the preparation of the oil phase for the production of theHIPE and the preparation of the water phase is generally required to becarried out in the neighborhood of normal room temperature.

In this respect, the inventions disclosed in the official gazette ofWO97/45456 and the official gazette of WO97/45479 have been aimed atstabilizing an HIPE and fulfilling the polymerization of an HIPE at ahigh temperature. The stabilization attained by the inventions does notdeserve to be rated as fully satisfactory because their methods actuallydegrade the emulsifying power during the steps of emulsification andpolymerization and induce separation of water. Particularly, the methodtaught in the official gazette of WO97/45456, when expected to attainthe emulsification by using a water phase heated at a temperature higherthan 40° C., has the possibility of degrading the HIPE in stability,entailing separation of a large amount of water during the course ofemulsification or polymerization, and inducing the polymer material tosuffer from degradation of performance.

The produced porous cross-linked polymer can be used as a soundinsulating material or a heat insulating material for the purpose ofabsorbing sound or heat, as a chemical impregnating substrate for thepurpose of imbibing an aromatic material or a detergent, and as anaborbing material for oil or organic solvent. It can also be used as asanitary material as in disposable diapers or sanitary articles or as acosmetic or medical material for applications not fated to create directcontact with the human system. In this case, the surface of the porouscross-linked material as a finished product is required to reduce thestimulus to the skin to the fullest possible extent for the purpose ofpreventing the user from forming skin rash or experiencing unpleasantfeeling. When the charged raw materials are caused as by degeneration toemit offensive odor or produce stimulus, the offensive odor or thestimulus possibly persists in the product. An effort to remove it fromthe product gives rise to the necessity of fortifying the washing step.Since the HIPE inherently has a water content in the range of1,000-25,000 (v/v) % and the preparation of the HIPE itself requires alarge amount of water to be used, it is necessary to decrease thewashing water to be used to the fullest possible extent. Particularly,the porous cross-linked polymer has a large surface area for contactwith the ambient air and, therefore, requires a large amount of washingwater to be thoroughly cleaned. This fact implies the disposal andexpulsion of a large amount of waste water and brings such adverseeffects as increasing the cost of production and augmenting the load onthe environment.

DISCLOSURE OF THE INVENTION

The present inventor has pursued a diligent study with a view todeveloping a method for producing a porous cross-linked polymer materialin a very short period of time in accordance with the principle of theHIPE method. It was consequently found that when a polyglycerine fattyacid ester is used as a surfactant and a consequently obtained HIPE ispolymerized at a high temperature, a porous cross-linked polymermaterial suffering separation of waster only in small amount is obtainedin a short time and a finally obtained porous cross-linked polymermaterial excels in absorption properties. This invention has beenperfected based on this discovery. Specifically, this invention is aimedat providing the following item (1).

(1) In producing a porous cross-linked polymer by forming an HIPE andsubsequently polymerizing the HIPE, a method for the production of aporous cross-linked polymer material which comprises a step ofpolymerizing the HIPE obtained in the presence of a polyglycerine fattyacid ester.

According to this invention, the HIPE can be polymerized in such aheretofore unforeseeable short span of time as not more than one hour,preferably not more than 30 minutes and the porous cross-linked polymermaterial excelling in absorbing properties can be efficiently produced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view illustrating an apparatus adapted forthe production of a porous cross-linked polymer and used in the workingexamples.

101 . . . HIPE, 102 . . . porous cross-linked polymer, 119 . . . HIPEsupplying device unit, 201 . . . endless belt type conveyr (furnishedwith drive conveying device), 203, 205 . . . sheet material, 207, 208 .. . unwinding roller, 209, 211 . . . roller, 212, 213 . . . rewindingroller, 215 . . . polymerization furnace, 217 . . . heating means, 219 .. . hot water shower.

BEST MODE OF EMBODYING THE INVENTION

This invention, in producing a porous cross-linked polymer by forming anHIPE and subsequently polymerizing the HIPE, primarily concerns a methodfor producing a porous cross-linked polymer material which comprises astep of polymerizing the HIPE obtained in the presence of apolyglycerine fatty acid ester.

Here, one example of the mode of continuously producing a porouscross-linked polymer material by polymerizing an HIPE will be describedbelow with the aid of a flow of FIG. 1. As illustrated in FIG. 1, anHIPE 101 is continuously supplied from an HIPE supplying part 119 onto asheet material 203 and formed in the shape of a sheet by adjusting theset height of a roller 209. The rotating speeds of an unwinding and arewinding roller 208, 212 are so controlled as to synchronize the sheetmaterial 203 with a conveyor belt 201. A sheet material 205, whilecontinuing application of tension to the HIPE 101 so as to fix thethickness thereof, has the rotating speed thereof controlled with theroller 209 and a roller 211 and an unwinding and a rewinding roller 207and 213. In a polymerization furnace 215, the HIPE 101 is polymerized toafford a porous cross-linked polymer material 102 by the operation of aheating means 219 formed of a hot water shower and disposed below theconveyor belt 201 and a heating means 217 formed of a hot windcirculating device and disposed above the conveyor belt 201. Then, bypeeling the upper and lower sheet materials 203 and 205, the porouscross-linked polymer material 102 can be obtained. Now, this inventionwill be described in detail below.

I. Preparation of HIPE

(1) Raw Materials Used for HIPE

The raw materials to be used for an HIPE are only required to contain(a) a polymerizing monomer, (b) a cross-linking monomer, and (c) asuffactant, namely a polyglycerine fatty acid ester, as an essentialcomponent for forming an oil phase and (d) water as an essentialcomponent for forming a water phase. They may further contain, whennecessary, (e) a polymerization initiator, (f) a salt, and (g) otheradditives as arbitrary component for forming the oil phase and/or thewater phase.

(a) Polymerizing Monomer

The monomer composition essential for the composition of the HIPEmentioned above is a polymerizing monomer possessing one polymerizingunsaturated group in the molecule thereof. Though it does not need to beparticularly discriminated but has only to be capable of beingpolymerized in a dispersion or an HIPE and allowed to form an emulsionconsequently. It preferably contains a (meth)acrylic ester at leastpartly, more preferably contains not less than 20 mass % of the(meth)acrylic ester, and particularly preferably contains not less than35 mass % of the (meth)acrylic ester. When the (meth)acrylic ester iscontained as a polymerizing monomer possessing one polymerizingunsaturated group in the molecule thereof proves advantageous becausethe produced porous cross-linked polymer abounds in flexibility andtoughness.

As concrete examples of the polymerizable monomer which is usedeffectively in this invention, allylene monomers such as styrene;monoalkylene allylene monomers such as ethyl styrene, α-methyl styrene,vinyl toluene, and vinyl ethyl benzene; (meth)acrylic esters such asmethyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate,isobutyl (meth)acrylate, isodecyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate,cyclohexyl (meth)acrylate, and benzyl (meth)acrylate;chlorine-containing monomers such as vinyl chloride, vinylidenechloride, and chloromethyl styrene; acrylonitrile compounds such asacrylonitrile and methacrylonitrile; and vinyl acetate, vinylpropionate, N-octadecyl acrylamide, ethylene, propylene, and butene maybe cited. These polymerizable monomers may be used either singly or inthe form of a combination of two or more members.

The content of the polymerizing monomer is preferred to be in the rangeof 10-99.9 mass %, based on the total mass of the monomer compositionconsisting of the polymerizing monomer and across-linking monomer. Thereason for this range is that the produced porous cross-lined polymer isenabled to acquire pores of minute diameters. The range is morepreferably 30-99 mass % and particularly preferably 30-70 mass %. If thecontent of the polymerizing monomer is less than 10 mass %, the producedporous cross-linked polymer will be possibly friable and deficient inwater absorption ratio. Conversely, if the content of the polymerizingmonomer exceeds 99.9 mass %, the porous cross-linked polymerconsequently produced will be possibly deficient in strength and elasticrecovery power and incapable of securing sufficient amount of waterabsorbed and sufficient velocity of water absorption.

(b) Cross-linking Monomer

The other monomer composition essential for the composition of the HIPEmentioned above is a cross-linking monomer possessing at least twopolymerizing unsaturated groups in the molecule thereof. Similarly tothe polymerizing monomer mentioned above, it does not need to beparticularly discriminated but has only to be capable of beingpolymerized in a dispersion or a water-in-oil type high internal phaseemulsion and allowed to form an emulsion consequently.

As concrete examples of the cross-linking monomer which is. effectivelyusable herein, aromatic monomers such as divinyl benzene, trivinylbenzene, divinyl toluene, divinyl xylene, p-ethyl-vinyl benzene, divinylnaphthalene, divinyl alkyl benzenes, divinyl phenanthrene, divinylbiphenyl, divinyl diphenyl methane, divinyl benzyl, divinyl phenylether, and divinyl diphenyl sulfide; oxygen-containing monomers such asdivinyl furan; sulfur-containing monomers such as divinyl sulfide anddivinyl sulfone; aliphatic monomers such as butadiene, isoprene, andpentadiene; and esters of polyhydric alcohols with acrylic acid ormethacrylic acid such as ethylene glycol di(meth)acrylate, diethyleneglycol di(meth)acrylate, triethylene glycol di(meth)acrylate,polyethylene glycol di(meth)acrylate, 1,3-butane diol di(meth)acrylate,1,4-butane diol di(meth)acrylate, 1,6-hexane diol di(meth)acrylate,octane diol di(meth)acrylate, decane diol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylol propane tri(meth)acrylate,pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, dipentaerythritol di(meth)acrylate,dipentaerythritol tri(meth)acrylate, dipentaerythritoltetra(meth)acrylate, N,N′-methylene bis(meth)acryl amide, triallylisocyanurate, triallyl amine, tetraallyloxy ethane, hydroquinone,catechol, resorcinol, and sorbitol may be cited. These cross-linkingmonomers may be used either singly or in the form of a combination oftwo or more members.

The content of the cross-linking monomer is properly in the range of0.1-90 mass %, preferably 1-70 mass %, and particularly preferably 30-70mass %, based on the total mass of the monomer composition consisting ofthe polymerizing monomer mentioned above and the cross-linking monomermentioned above. If the content of the cross-linking monomer is lessthan 0.1 mass %, the produced porous cross-linked polymer will possiblybe deficient in strength and elastic recovery force, unable to effectabsorption sufficiently per unit volume or unit mass, and incapable ofsecuring absorption in a sufficient amount at a sufficient velocity.Conversely, if the content of the cross-linking monomer exceeds 90 mass%, the porous cross-linked polymer produced consequently will possiblybe friable and deficient in water absorption ratio.

(c) Surfactant

The surfactant mentioned above is a polyglycerine fatty acid ester. Thispolyglycerine fatty acid ester does not need to be particularlyrestricted but is only required to be such that the polyglycerineforming the ester is an oligomer of not less than 3 glycerine units. Thedemarcation of not less than 3 glycerine units is based on theascertainment that while the use of a fatty acid ester of glycerin aloneor glycerin dimer produces no sufficient emulsifying power, the use of afatty acid ester of an oligomer of three or more glycerin units allowsan HIPE to be stabilized even at high temperatures and consequentlywarrants production of a polymer entailing separation of water only in asmall amount and excelling in the ratio of free swelling. The fatty acidis only required to be bound at a rate of not less than one molecule tothe polyglycerine and does not need to be bound to all the hydroxylgroups. The size of the polyglycerine is preferably an oligomer in therange of 3-10 glycirine units, more preferably in the range of 6-10glycerine units. The fatty acid forming the polyglycerine fatty acidester is preferably a fatty acid of 6-28 carbon atoms, more preferably afatty acid of 12-24 carbon atoms, and particularly preferably a fattyacid of 16-20 carbon atoms. Such a fatty acid may be possessed of abranched chain. The fatty acid may be a saturated fatty acid or anunsaturated fatty acid so long as the number of carbon atoms falls inthe range mentioned above. The preferred linear chain fatty acidsinclude lauric acid, myristic acid, palmitic acid, stearic acid, oleicacid, docosanoic acid, tetracosanoic acid, and ricinoleic acid, forexample. The preferred branched chain fatty acids include isostearicacid, for example.

As concrete examples of the polyglycerine fatty acid esters which areusable in this invention, tetraglyceryl monostearate, tetraglycerylmonooleate, tetraglyceryl tristearate, tetraglyceryl pentastearate,tetraglyceryl pentaoleate, tetraglyceryl monolaurate, tetraglycerylmonomyristate, hexaglyceryl monostearate, hexaglyceryl monooleate,hexaglyceryl tristearate, hexaglyceryl pentastearate, hexaglycerylpentaoleate, hexaglyceryl polyricinolate, decaglyceryl monolaurate,decaglyceryl monostearate, decaglyceryl monomyristate, decaglycerylmonoiso-stearate, decaglyceryl monooleate, decaglycryl monolinolate,decaglyceryl distearate, decaglyceryl diisostearate, decaglyceryltristearate, decaglyceryl trioleate, decaglyceryl trioleate,decaglyceryl pentastearate, decaglyceryl pentaisostearate, decaglycerylpentaoleate, decaglyceryl heptastearate, decaglyceryl heptaoleate,decaglyceryl decastearate, decaglyceryl decaisostearate, anddecaglyceryl decaoleate may be cited. This invention particularlyprefers to use decaglyceryl trioleate. Two or more of these olyglycerinfatty acid esters may be used in combination. Such combined use possiblyresults in improving a given HIPE in stability.

As the surfactant, such a polyglycerine fatty acid ester may be usedalone or in combination with some other surfactant. When thepolyglycerine fatty acid ester and other surfactant are used incombination, the ratio of the polyglycerine fatty acid ester to thewhole surfactant is preferably not less than 50 mass. %, more preferablynot less than 70 mass. %. As concrete examples of the surfactant whichcan be used in combination with the polyglycerine fatty acid ester, thenonionic surfactants, anionic surfactants, cationic surfactants, andamphoteric surfactants which are known to the art may be cited.

Among these surfactants, as concrete examples of the nonionicsurfactant, nonyl phenol polyethylene oxide adduct; block polymer ofethylene oxide and propylene oxide; sorbitan fatty acid esters such assorbitan monolaurate, sorbitan monomyristylate, sorbitan monopalmitate,sorbitan monostearate, sorbitan tristearate, sorbitan monooleate,sorbitan trioleate, sorbitan sesquioleate, and sorbitan distearate;glycerin fatty acid esters such as glycerol monostearate, glycerolmonooleate, diglycerol monooleate, and self-emulsifying glycerolmonostearate; polyoxyethylene alkyl ethers such as polyoxyethylenelauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearylether, polyoxyethylene oleyl ether, and polyoxyethylene higher alcoholethers; polyoxyethylene alkylaryl ethers such as polyoxyethylene nonylphenyl ether; polyoxyethylene sorbitan fatty acid esters such aspolyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitanmonomyristylate, polyoxyethylene sorbitan monopalmitate, polyoxyethylenesorbitan monostearate, polyoxyethylene sorbitan tristearate,polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitantrioleate; polyoxyethylene sorbitol fatty acid esters such as tetraoleicacid polyoxyethylene sorbit; polyoxyethylene fatty acid esters such aspolyethylene glycol monolaurate, polyethylene glycol monostearate,polyethylene glycol distearate, and polyethylene glycol monooleate;polyoxyethylene alkyl amines; hydrogenated polyoxyethylene castor oil;and alkyl alkanol amides may be cited. These nonionic surfactants havingHLB values of not more than 10, more preferably in the range of 2-6,prove preferable. It is permissible to use two or more such nonionicsurfactants in combination. The combined use possibly results instabilizing the HIPE.

As concrete examples of the cationic surfactant, quaternary ammoniumsalts such as stearyl trimethyl ammonium chloride, ditallow dimethylammonium methyl sulfate, cetyl trimethyl ammonium chloride, distearyldimethyl ammonium chloride, and alkylbenzyl dimethyl ammonium chloride;alkyl amine salts such as coconut amine acetate and stearyl amineacetate; alkyl betaines such as lauryl trimethyl ammonium chloride,lauryl betaine, stearyl betaine, and lauryl carboxymethyl hydroxyethylimidazoliniumbetaine; and amine oxides such as lauryl dimethyl amineoxide may be cited. The use of the cationic surfactant can impartexcellent antibacterial properties to the porous cross-linked polymerwhen the polymer is used for an absorbent material, for example.

The anionic surfactant of a kind possessing an anionic moiety and anoil-soluble moiety can be advantageously used. As concrete examples ofanionic surfactant, such reactive anion emulsifiers possessed of adouble bond as, for example, alkyl sulfates such as sodium dodecylsulfate, potassium dodecyl sulfate, and ammonium alkyl sulfate; sodiumdodecyl polyglycol ether sulfate; sodium sulforicinoate; alkylsulfonates such as sulfonated paraffin salts; sodium dodecyl benzenesulfonate, alkyl sulfonates such as alkali metal sulfates of alkaliphenol hydroxyethylene; higher alkyl naphthalene sulfonates; fatty acidsalts such as naphthalene sulfonic acid formalin condensate, sodiumlaureate, triethanol amine oleate, and triethanol amine apiate;polyoxyalkyl ether sulfuric esters; sulfuric esters of polyoxyethylenecarboxylic ester and polyoxyethylene phenyl ether sulfuric esters;succinic acid dialkyl ester sulfonates; and polyoxy ethylene alkyl arylsulfates may be cited. An HIPE may be prepared by using an anionicsurfactant in combination with a cationic surfactant.

The combined use of the nonionic surfactant and the cationic surfactantmay possibly improve the HIPE in stability.

The content of the surfactant mentioned above is properly in the rangeof 1-30 mass parts, preferably 3-15 mass parts, based on 100 mass partsof the total mass of the monomer composition consisting of thepolymerizing monomer and the cross-linking monomer. If the content ofthe surfactant is less than 1 mass part, the shortage will possiblydeprive of the HIPE of stability of dispersion and prevent thesurfactant from manifesting the effect inherent therein sufficiently.Conversely, if the content of the surf actant exceeds 30 mass parts, theexcess will possibly render the produced porous cross-linked polymerunduly friable and fail to bring a proportionate addition to the effectthereof and do any good economically.

(d) Water

The water essential for the composition of the HIPE mentioned above maybe city water, purified water ordeionized water. Alternatively, with aview to utilizing to advantage the waste water resulting from theproduction of the porous cross-linked polymer, this waste water may beadopted in its unmodified form or after undergoing a prescribedtreatment.

The content of the water may be suitable selected, depending on the kindof use (such as, for example, an absorbent material, sound insulationmaterial, or filter) for which the porous cross-linked polymerpossessing continuous cells is intended. Since the hole ratio of theporous cross-linked polymer material is decided by varying the waterphase/oil phase (W/O) ratio of the HIPE, the amount of water to be usedis automatically decided by selecting the W/O ratio calculated toproduce a hole ratio which conforms to the use and the purpose of theproduced material.

(e) Polymerization Initiator

For the purpose of accomplishing the polymerization of an HIPE in a veryshort period of time as aimed at by this invention, it is advantageousto use a polymerization initiator. The polymerization initiator is onlyrequired to be suitable for use in the reversed phase emulsionpolymerization. It is not discriminated between the water-soluble typeand the oil-soluble type.

As concrete examples of the water-soluble polymerization initiator whichis used effectively herein, azo compounds such as2,2′-azobis(2-amidinopropane) dihydrochloride; persulfates such asammoniumpersulfate, potassiumpersulfate, and sodium persulfate;peroxides such as potassiumperacetate, sodiumperacetate,sodiumpercarbonate, potassiumperacetate may be cited. As concreteexample of the oil-soluble polymerization initiator which is usedeffectively herein, peroxide such as, cumenehydroperoxide,t-butylhydroperoxide, t-butylperoxide-2-ethylhexyanoate di-t-butylperoxide, diisopropyl benzene hydroperoxide, p-methane hydroperoxide,1,1,3,3-tetramethylbutyl hydroperoxide,2,5-dimethylhexane-2,5-dihydroperoxide, benzoyl peroxide, andmethylethyl ketone peroxide may be cited. These polymerizationinitiators may be used either singly or in the form of a combination oftwo or more members.

Combined use of two or more kinds of polymerization initiator havingdifferent 10 hour half period temperatures, i.e. the temperatures atwhich the concentrations of the relevant initiators are halved in 10hours proves advantageous. As a matter of course, it is permissible touse in combination the water-soluble polymerization initiator and theoil-soluble polymerization initiator.

The content of the polymerization initiator mentioned above is properlyin the range of 0.05-25 mass parts, preferably 1.0-10 mass parts, basedon 100 mass parts of the total mass of the monomer compositionconsisting of a polymerizing monomer and a cross-linking monomer, thoughit is variable with the combination of the polymer composition and thepolymerization initiator. If the content of the polymerization initiatoris less than 0.05 mass part, the shortage will be at a disadvantage inincreasing the amount of the unaltered monomer component andconsequently increasing the residual monomer content in the producedporous cross-linked polymer. Conversely, if the content of thepolymerization initiator exceeds 25 mass parts, the excess will be at adisadvantage in rendering the polymerization difficult to control anddegrading the mechanical property of the produced porous cross-linkedpolymer.

Alternatively, a redox polymerization initiator formed by combining thepolymerization initiator mentioned above with a reducing agent may beused. In this case, the polymerization initiator to be used herein doesnot need to be discriminated between the water-soluble type and theoil-soluble type. It is permissible to use a water-soluble redoxpolymerization initiator and an oil-soluble redox polymerizationinitiator in combination.

In the reducing agents, as concrete examples of the water-solublereducing agents, sodium hydrogen sulfite, potassium hydrogen sulfite,sodium thiosulfate, potassium thiosulfate, L-ascorbic acid, ferroussalts, formaldehyde sodiumsulfoxylate, glucose, dextrose, triethanolamine, and diathanol amine may be cited. As concrete examples of theoil-soluble reducing agent, dimethyl aniline, tin octylate, and cobaltnaphthenate may be cited. These redox polymerization initiator typereducing agents may be used either singly or in the form of a mixture oftwo or more members.

The ratio of the reducing agent contained in the redox polymerizationinitiator mentioned above (mass ratio), i.e. the polymerizationinitiator (oxidizing agent)/reducing agent, is in the approximate rangeof 1/0.01-1/10, preferably 1/0.2-1/5.

The polymerization initiator (inclusive of the redox polymerizationinitiator) is only required to be present at least during the course ofthe polymerization of an HIPE. It may be added to the oil phase and/orthe water phase {circle around (1)} prior to the formation of an HIPE,At simultaneously with the formation of an HIPE, or {circle around (2)}after the formation of an HIPE. In the case of the redox polymerizationinitiator, the polymerization initiator (oxidizing agent) and thereducing agent may be added at different times.

(f) Salt

The salt as an arbitrary component for the composition of the HIPEmentioned above may be used when it is necessary for improving thestability of the HIPE.

As concrete examples of the salt of this nature, halogenides, sulfates,nitrates, and other similar water-soluble salts of alkali metals andalkaline earth metals such as calcium chloride, sodium sulfate, sodiumchloride, and magnesium sulfate may be cited. These salts may be usedeither singly or in the form of a combination of two or more members.Such a salt is preferred to be added in the water phase. Among othersalts mentioned above, polyvalent metal salts prove particularlyadvantageous from the viewpoint of the stability of the HIPE during thecourse of polymerization.

The content of the salt mentioned above is proper in the range of 0.1-20mass parts, preferably 0.5-10 mass parts, based on 100 mass parts. Ifthe content of the salt exceeds 20 mass parts, the excess will be at adisadvantage in suffering the waste water squeezed out of the HIPE tocontain the water in an unduly large amount, boosting the cost for thedisposal of the waste water, failing to bring a proportional addition tothe effect, and not doing any good economically. If the content is lessthan 0.1 mass part, the shortage will possibly prevent the effect of theaddition of the salt from being fully manifested.

(g) Other Additive

Varying other additive which are capable of improving the conditions ofproduction, the property of HIPE, and the performance of the porouscross-linked polymer by imparting the performance and the function oftheir own, they may be suitably used herein. For example, a base and/ora buffer may be added for the purpose of adjusting the pH value. Thecontent of the other additive may be selected within such a range thatthe additive used may fully manifest the performance, function, andfurther the economy commensurate with the purpose of addition. As suchadditives, activated carbon, inorganic powder, organic powder, metallicpowder, deodorant, antibacterial agent, antifungi agent, perfume andother highly polymerized compounds may be cited.

(2) Method for Preparation of HIPE

The method for production of the HIPE which can be used in thisinvention does not need to be particularly discriminated. Any of themethods for production of HIPE heretofore known to the art may besuitably used. A typical method for the production of interest will bespecifically described below.

First, a polymerizing monomer, a cross-linking monomer, and a surfactantas essential components and further an oil-soluble polymerizationinitiator (inclusive of an oil-soluble redox polymerization initiator)and other additive as optional components for the formation of an oilphase prepared in respectively specified amounts mentioned above arestirred at a prescribed temperature to produce a homogeneous oil phase.

Meanwhile, water as an essential component and further a water-solublepolymerization initiator (inclusive of a water-soluble redoxpolymerization initiator), salts, and other additive as optionalcomponents for the formation of a water phase prepared in respectivelyspecified amounts are stirred and heated to a prescribed temperature inthe range of 30-95° C. to produce a homogeneous water phase.

Then, the oil phase which is the mixture of the monomer component, surfactant, etc. and the water phase which is the mixture of water,water-soluble salt, etc., both prepared as described above are joined,mixed and stirred efficiently for exertion of proper shearing force andinduction of emulsification at the temperature for the formation of anHIPE (emulsifying temperature) which will be described specificallyhereinbelow to accomplish stable preparation of an HIPE. As a means forstirring and mixing the water phase and the oil phase particularly forthe table preparation of the HIPE, the method which comprises keepingthe oil phase stirred and continuously adding the water phase to thestirred oil phase over a period of several minutes to some tens ofminutes. Alternatively, the HIPE aimed at may be produced by stirringand mixing part of the water phase component and the oil phase componentthereby forming an HIPE resembling yogurt and continuing the stirringand mixing operation while adding the remaining portion of the waterphase component to the yogurt-like HIPE.

(3) Water Phase/oil Phase (W/O) Ratio

The water phase/oil phase (W/O) ratio (mass ratio) of the HIPE which isobtained as described above does not need to be particularly limited butmay be properly selected to suit the purpose for which the porouscross-linked polymer material possessed of open cells is used (such as,for example, water absorbent, oil absorbent, sound insulating material,and filter). It is only required to be not less than 3/1 as specifiedabove and is preferred to fall in the range of 10/1-250/1, particularly10/1-100/1. If the W/O ratio is less than 3/1, the shortage will bepossibly at a disadvantage in preventing the porous cross-linked polymermaterial from manifesting a fully satisfactory ability to absorb waterand energy, lowering the degree of opening, and causing the surface ofthe produced porous cross-linked polymer material to suffer from undulylow degree of opening and fail to exhibit a fully satisfactorypermeability to liquid. The hole ratio of the porous cross-linkedpolymer material is decided by varying the W/O ratio. Thus, the W/Oratio is preferred to be selected so as to impart to the produced porouscross-linked polymer material a hole ratio conforming to the use and thepurpose. When the product is used as a varying absorbent material suchas disposable diaper or sanitary article, for example, the W/O ratio ispreferred to fall in the approximate range of 10/1-100/1. Incidentally,the HIPE which is obtained by stirring and mixing the water phase andthe oil phase is generally a white highly viscous emulsion.

(4) Apparatus for Production of HIPE

The apparatus for the production of the HIPE mentioned above does notneed to be particularly discriminated. Any of the apparatuses for theproduction of the porous cross-linked polymer material which have beenheretofore known to the art may be used. For example, the stirringdevice (emulsifier) to be used for mixing and stirring the water phaseand the oil phase may be selected from among the stirring devices andthe kneading devices which have been heretofore known to the art. Asconcrete examples of the stirring device, stirring devices using vanesof the propeller type, the paddle type, and the turbine type,homomixers, line mixers, and pin mills may be cited.

(5) Forming Temperature of HIPE

The formation (emulsification) of an HIPE is generally carried out at atemperature exceeding 20° C. and approximating closely to thepolymerization temperature. In order for the porous cross-linked polymermaterial to be obtained in a short time efficiently, it is important toform an HIPE at a high temperature approximating closely to theemulsification temperature. Because of the difficulty encountered inobtaining an HIPE by stable emulsification at an elevated temperature,it has been heretofore customary to form an HIPE in the neighborhood ofroom temperature and polymerize this HIPE at a temperature elevated bysome tens of degrees C. Since the HIPE which contains water in a largeamount has a large thermal capacity, the time required for thetemperature elevation mentioned above forms a major cause for loweringthe productivity of the porous cross-linked polymer material. Since themethod of this invention is capable of stably forming an HIPE even at ahigh temperature, it can form the HIPE at a temperature equivalent to ornear the polymerization temperature and can eliminate the defects of theconventional method. Specifically, the forming temperature of the HIPEis preferably in the range of 40-100° C., more preferably in the rangeof 70-100° C., and particularly preferably in the range of 80-100° C. Itis commendable to form an HIPE aimed at by adjusting the temperature ofan oil phase and/or a water phase in advance to a prescribed formingtemperature (emulsifying temperature) and stirring and mixing the twophases till they are emulsified. In the preparation (formation) of theHIPE, however, since the water phase is in a large amount, it may besafely concluded preferable to have the temperature of at least thewater phase adjusted to the prescribed forming temperature (emulsifyingtemperature).

II. Production of Porous Cross-linked Polymer Material

(1) Addition of Polymerization Initiator

(a) Time for Addition of Polymerization Initiator

This invention contemplates {circle around (1)} adding a polymerizationinitiator to the water phase and/or the oil phase and mixing them priorto the formation of an HIPE, {circle around (2)} simultaneously addingthe polymerization initiator with the formation of the HIPE, or Admaking this addition subsequently to the formation of the HIPE.

(b) Method for Addition of Polymerization Initiator

It is convenient to add preparatorily the polymerization initiator tothe oil phase when the polymerization initiator or the reducing agent isan oil-soluble type or to the water phase when it is in a water-solubletype. Alternatively, the oil-soluble polymerization initiator (oxidizingagent) or the reducing agent may be added in an emulsified form, forexample, to the water phase.

(c) Form of Use of Polymerization Initiator

The polymerization initiator may be used in an undiluted form, in theform of a solution in water or an organic solvent, or in the form of adispersion. When the addition is made either simultaneously with orsubsequently to the formation of the HIPE, it is important that theadded polymerization initiator be quickly and homogeneously mixed withthe HIPE for the purpose of avoiding the otherwise possibleheterogeneous polymerization of the monomer component. Further, the HIPEwhich has been mixed with the polymerization initiator is quicklyintroduced into a polymerization vessel or a continuous polymerizingdevice as means for polymerization. It is commendable from this point ofview to insert a path for the introduction of a polymerization initiatorsuch as a reducing agent or an oxidizing agent in the path extendingfrom the emulsifying device for preparing the HIPE through thepolymerization vessel or the continuous polymerizing device, adding thepolymerization initiator via the path to the HIPE, and mix them by meansof a line mixer.

If the HIPE which contains the polymerization initiator has a smalldifference between the emulsifying temperature and the polymerizingtemperature thereof, the closeness of the emulsifying temperature to thepolymerizing temperature will possibly set the polymerizing monomer orthe cross-linking monomer polymerizing during the course of theemulsification and suffer the resultant polymer to impair the stabilityof the produced HIPE. Thus, the method of adding the reducing agent orthe oxidizing agent or other polymerization initiator to the HIPEimmediately prior to the polymerization, i.e. the method of {circlearound (2)} or {circle around (3)} mentioned above, proves advantageous.

The amount of the polymerization initiator to be used herein equals thatin the method described above under the title of the method forpreparation of HIPE.

(2) Polymerization of HIPE

(a) Method for Polymerization

Next, the method for polymerizing the HIPE mentioned above does not needto be particularly restricted but may be properly selected from amongthe known methods for the polymerization of an HIPE. Generally, the HIPEis polymerized by the method of stationary polymerization under theconditions which are incapable of breaking the structure of water dropshighly dispersed in the oil of the HIPE. The polymerization in this casemay be performed in a batch pattern which consists in polymerizing onebatch after another of HIPE or in a continuous pattern which consists incontinuously feeding an HIPE and superposing one layer on another of theHIPE.

To harness the effect of quick polymerization at an elevated temperaturewhich characterizes this invention, the polymerization of an HIPE iscarried out more preferably by the continuous method than the batchmethod because the former method is capable of elevating the temperatureof the HIPE easily. It is advantageous to adopt, for example, the methodof continuous polymerization which consists in continuously forming anHIPE in the form of a layer on a belt in motion and polymerizing thelayer of the HIPE. To be specific, for the continuous polymerization ofa porous cross-linked polymer in the shape of a sheet, a method whichcomprises continuously supplying an HIPE onto the belt in motion of abelt conveyor so constructed as to have the surface thereof heated witha heating device and forming the HIPE in the shape of a flat and smoothsheet and polymerizing it is available, for example. When the surface ofthe conveyor which is fated to contact the emulsion is flat and smooth,a continuous sheet of a necessary thickness may be obtained by supplyingthe HIPE in a prescribed thickness onto the belt. Since this inventionis capable of preparing an HIPE at a high temperature, the method ofcontinuous polymerization which continuously polymerizes an HIPE is atan advantage in heightening the efficiency of production and permittingthe effect of shortening the polymerization time to be utilized mosteffectively. Moreover, the act of polymerizing an HIPE in the form of asheet and meantime conveying it horizontally proves to be anadvantageous operation even in consideration of the fact that the HIPEis possessed of a comparatively brittle quality which permits the oilphase and the water phase thereof to be readily deflected and separatedin the vertical direction. Even in this case, it is permissible topolymerize an HIPE in the form of a block or a sheet and then fabricatethe block or the sheet in any arbitrary form by cutting it into sliceseach measuring 5 mm in thickness, for example.

(b) Polymerization Temperature

The polymerization temperature of the HIPE is preferred to be as high aspermissible for the purpose of enabling the polymerization to becompleted in a short time. Since the method of this invention isincapable of impairing the stability of the HIPE even at hightemperatures, the polymerization temperature can be selected more freelythan when a known emulsifier is used. The polymerization temperature ispreferably in the range of 70-150° C., more preferably in the range of75-110° C., and particularly preferably in the range of 85-100° C.Further, the polymerization temperature may be varied in two stages orin more stages during the course of the polymerization.

(c) Polymerization Time

The polymerization time for the HIPE in this invention is in the rangeof 1 minute-20 hours, preferably within one hour, more preferably within30 minutes, and particularly preferably in the range of 1-20 minutes. Ifthe polymerization time exceeds 20 hours, the excess will be possibly ata disadvantage commercially in degrading the productivity. Conversely,if the polymerization time is less than 1 minute, the shortage willpossibly prevent the porous cross-linked polymer material from acquiringsufficient strength. Of course, this invention does exclude the use of alonger polymerization time than the range mentioned above.

(d) Polymerizing Device

The polymerizing device which can be used for this invention does notneed to be particularly restricted. From the known chemical devices, adevice which fits the relevant method of polymerization may be selectedand used or, when necessary, may be used as suitably modified. For thebatch polymerization, a polymerization vessel so shaped as to fit thepurpose of use of the produced polymer can be used. For the continuouspolymerization, a belt conveyor type continuous polymerizing devicefurnished with a compressing roller can be used. Some of these devicesare provided with a heating means and a controlling means suitable forthe relevant method of polymerization such as, for example, an activethermal energy ray such as microwave or near infrared ray which canutilize a radiation energy or a heating means capable of quicklyelevating temperature with a thermal medium such as hot water or hotwind, for example. Such additional means need not be limited to thosementioned above. In the case of performing batch polymerization, theupper and lower surfaces of the mass of the HIPE placed in thepolymerization vessel are preferred not to be exposed to the ambientair, particularly to the oxygen contained in the ambient air, betweenthe time the polymerization is initiated and the time it is completed.These surface parts abhor the ambient air because they are capable ofstrictly securing the open cell structure. In the case of the beltconveyor type continuous polymerization, for example, it is commendableto spread a PET film on the belt conveyor serving the purpose ofsupplying an HIPE and, after the supply of the HIPE, immediately overlaythe HIPE with a sealing material such as a PET film to seal the HIPEfrom the ambient air. These polymerizing devices do not need to bediscriminated on account of the kind of material to be used therefore.They may be made of such metals as aluminum, iron, and stainless steel,such synthetic resins as polyethylene, polypropylene, fluorine resin,polyvinyl chloride, and unsaturated polyester resin, and suchfiber-reinforced resins as the synthetic resins mentioned abovereinforced with glass fibers or carbon fibers, for example.

(3) Step of Aftertreatment (Conversion into Finished Product) AfterFormation of Porous Cross-linked Polymer Material

(a) Dehydration

The porous cross-linked polymer material formed in consequence of thecompletion of polymerization is normally dehydrated by compression,aspiration under reduced pressure, or the combination thereof. By thisdehydration, generally 50-98% of the water used is removed and theremainder thereof is left adhering to the porous cross-linked polymermaterial.

The ratio of dehydration is properly set to suit the purpose for whichthe produced porous cross-linked polymer material is used. Generally,the water content in the porous cross-linked polymer material in aperfectly dried state is set at a level in the range of 1-10 g,preferably 1-5 g, per g of the polymer material.

(b) Compression

The porous cross-linked polymer of this invention can be obtained in aform compressed to one of several divisions of the original thickness.The compressed sheet has a smaller inner volume than the original porouscross-linked polymer and permits a decrease in the cost oftransportation or storage. The porous cross-linked polymer in thecompressed state is characterized by being disposed to absorb water whenexposed to a large volume of water and resume the original thickness andexhibiting the ability to absorb water at a higher speed than theoriginal polymer.

From the viewpoint of saving the space for transportation or storage andfacilitating the handling, it is effective to compress the polymer tonot more than ½ of the original thickness. Preferably, the compressionis made to not more than ¼ of the original thickness.

(c) Cleaning

For the purpose of improving the surface condition of the porouscross-linked polymer, the porous cross-linked polymer may be washed withpure water, an aqueous solution containing an arbitrary additive, or asolvent.

(d) Drying

The porous cross-linked polymer obtained by the preceding steps, whennecessary, may be dried by heating as with hot air or microwaves or maybe moistened for adjustment of the water content.

(e) Cutting

The porous cross-linked polymer obtained by the preceding steps, whennecessary, may be cut in expected shape and size and fabricated into afinished product fitting the purpose of use.

(f) Impregnation

The polymer may be endowed with functionality by being impregnated witha detergent or an aromatic agent.

EXPERIMENTS

Now, this invention will be described more specifically below withreference to working example. The properties of the porous cross-linkedpolymer material reported in these working examples were determined andrated as follows.

(1) Ratio of Water Separation

The ratio of water separation (%) was determined by recovering theseparated water occurring after the polymerization by decantation fromthe polymerization vessel, weighing the recovered water, and performingcalculation of the following formula 1 using the results of theweighing.

Ratio of water separation (%)=(Mass of separated water/mass of waterphase used)×100  Formula 1

(2) Ratio of Free Swelling

The ratio of free swelling (g/g) of a given porous cross-linked polymerwas determined by cutting a sample measuring a square of 1 cm from thepolymer, drying and weighing this sample in advance, immersing thesample in an ample amount of purified water, allowing the sample nowswelled with the absorbed purified water to stand at rest for 30 secondson a glass filter measuring 120 m min diameter and 5 m min thickness(made by Duran Corp. and sold under the product code of #0), drainingthe wet sample, measuring the impregnated sample for weight, andcalculating the following formula 2 using the results of themeasurement.

Ratio of free swelling (g/g)=((Mass of sample after absorbing water-massof sample before absorbing water)/(Mass of sample before absorbingwater)  Formula 2

EXAMPLE 1

The water phase to be used for the process of continuous emulsificationfor the formation of an HIPE was prepared by dissolving 36.3 kg ofanhydrous potassium chloride and 568 g of potassium persulfate in 378liters of purified water. Then, the water phase was obtained by adding960 g of decaglyceryl trioleate to a mixture of 1600 g of styrene. Thewater phase was supplied at a temperature of 80° C. at a flow volume of56.5 cm³/s and the oil phase was supplied at a temperature of 22° C. ata flow volume of 1.13 g/s separately to a dynamic mixing device andthese two phases in the dynamic mixing device were thoroughly mixed andpartly recycled with a pin impeller rotating at 1800 rpm. The resultantHIPE of a temperature of 79° C. was cast at a flow volume of 57.6 cm³/sinto the gap between the PET films attached to a device illustrated inFIG. 1. The cast HIPE, after having the thickness thereof adjusted to 5mm, was moved on an oblong plate, passed at a transferring speed of 15cm/min. through a polymerization furnace set in advance at an internaltemperature of 80° C., and polymerized for 60 minutes to obtain apolymer. No sign of water separation was observed on this polymer. Thepolymer thus obtained was dehydrated and dried to afford a porouscross-linked polymer material. This porous cross-linked polymer materialexhibited such a high ratio of free swelling as 47 g/g, indicating thatit had a satisfactory water absorbing property.

EXAMPLE 2

An HIPE was obtained by following the procedure of Example 1 while usinga water phase of a temperature of 85° C. in the place of the water phaseof a temperature of 80° C. The HIPE thus obtained was cast into the gapbetween the PET films attached to the device of FIG. 1. The cast HIPE,after having the thickness thereof adjusted to 5 mm, was moved on anoblong plate, passed at a transferring speed of 1.25 m/min. through apolymerization furnace set in advance at an inner temperature of 95° C.,and polymerized for 8 minutes to afford a polymer. No sign of waterseparation was observed on this polymer. The polymer thus obtained wasdehydrated and dried to obtain a porous cross-linked polymer material.This porous cross-linked polymer material exhibited such a high ratio offree swelling as 47 g/g, indicating that it had a satisfactory waterabsorbing property.

EXAMPLE 3

An HIPE was obtained by following the procedure of Example 1 while usinghexaglyceryl monooleate in the place of the decaglyceryl trioleate. TheHIPE thus obtained was cast into the gap between the PET films attachedto the device of FIG. 1. The cast HIPE, after having the thicknessthereof adjusted to 5 mm, was moved on an oblong plate, passed at atransferring speed of 30 cm/min. through a polymerization furnace set inadvance at an inner temperature of 80° C., and polymerized for 30 min.to afford a polymer. No sign of water separation was observed on thispolymer. The polymer thus obtained was dehydrated and dried to obtain aporous cross-linked polymer material. This porous cross-linked polymermaterial exhibited such a high ratio of free swelling as 47 g/g,indicating that it had a satisfactory water absorbing property.

EXAMPLE 4

An HIPE was obtained by following the procedure of Example 1. In aplastic container having an inner volume of 600 cc, 250 g the HIPE thusobtained was placed, sealed by closing the container with a stopper, andpolymerized by being kept immersed as held in the container in a waterbath set at 80° C. for 60 minutes to afford a polymer. No sign of waterseparation was observed on the polymer. The polymer thus obtained wassliced into pieces 5 mm in thickness and the sliced pieces weredehydrated and dried to afford a porous cross-linked polymer material.This porous cross-linked polymer material exhibited such a high ratio offree swelling as 47 g/g, indicating that it had a satisfactory waterabsorbing property.

COMPARATIVE EXAMPLE 1

An HIPE was obtained by following the procedure of Example 1 while usingglyceryl monooleate in the place of the decaglyceryl trioleate. The HIPEthus obtained was cast into the gap between the PET films attached tothe device of FIG. 1. The cast HIPE, after having the thickness thereofadjusted to 5 mm, was moved on an oblong plate, passed at a transferringspeed of 15 cm/min. through a polymerization furnace set in advance atan inner temperature of 80° C., and polymerized for 60 min. to afford apolymer. A sign of water separation was observed on this polymer. Thepolymer thus obtained was dehydrated and dried to obtain a porouscross-linked polymer material. This porous cross-linked polymer materialexhibited such a low ratio of free swelling as 30 g/g, indicating thatit had an inferior water absorbing property.

COMPARATIVE EXAMPLE 2

An HIPE was obtained by following the procedure of Example 1 while usingglyceryl monooleate in the place of the decaglyceryl trioleate. In aplastic container having an inner volume of 600 cc, 250 g the HIPE thusobtained was placed, sealed by closing the container with a stopper, andpolymerized by being kept immersed as held in the container in a waterbath set at 80° C. for 60 minutes to afford a polymer. A sign of waterseparation was observed on the polymer. The ratio of the waterseparation was found to be 35%. The polymer thus obtained was slicedinto pieces 5 mm in thickness and the sliced pieces were dehydrated anddried to afford a porous cross-linked polymer material. This porouscross-linked polymer material exhibited such a low ratio of freeswelling as 30 g/g, indicating that it had an inferior water absorbingproperty.

COMPARATIVE EXAMPLE 3

An HIPE was obtained by following the procedure of Example 1 while usingdiglyceryl monooleate in the place of the decaglyceryl trioleate. In aplastic container having an inner volume of 600 cc, 250 g the HIPE thusobtained was placed, sealed by closing the container with a stopper, andpolymerized by being kept immersed as held in the container in a waterbath set at 80° C. for 60 minutes to afford a polymer. A sign of waterseparation was observed on the polymer. The ratio of the waterseparation was found to be 15%. The polymer thus obtained was slicedinto pieces 5 mm in thickness and the sliced pieces were dehydrated anddried to afford a porous cross-linked polymer material. This porouscross-linked polymer material exhibited such a low ratio of freeswelling as 40 g/g, indicating that it had an inferior water absorbingproperty.

Industrial Applicability

According to this invention, the HIPE can be polymerized in such aheretofore unforeseeable short span of time as not more than one hour,preferably not more than 30 minutes and the porous cross-linked polymermaterial excelling in absorbing properties can be efficiently produced.

What is claimed is:
 1. In producing a porous cross-linked polymer byforming a water-in-oil type high internal phase emulsion andsubsequently polymerizing the emulsion, a method for the production of aporous cross-linked polymer material which comprises a step ofpolymerizing a water-in-oil type high internal phase emulsion obtainedin the presence of a polyglycerine fatty acid ester.
 2. A methodaccording to claim 1, wherein the polyglycerine forming thepolyglycerine fatty acid ester is an oligomer of 3-10 glycerine units.